Project Summary The obesity and its associated syndromes affect millions of people and impose a huge burden on our society. Thus, there is an urgent need to develop novel prevention and treatment methods for obesity. Hypothalamic neurocircuitry plays a major role in central regulation of energy homeostasis that is known to have tremendous impact on pathogenesis of obesity and diabetes. The majority of hypothalamic neurons release fast-acting neurotransmitters such as glutamate and GABA, as well as express their receptors that are critical for inter- neuronal communication. Therefore, understanding the function of glutamate and GABA in hypothalamic neurocircuits is key to identify important neural pathways that can be ultimately targeted for obesity prevention and therapeutics. Specifically, the arcuate nucleus, a critical region in hypothalamic regulation of energy balance, primarily consists of GABAergic neurons. However, with the exception of AgRP neurons, the function GABA release from arcuate GABAergic neurons is not clear. Recent studies suggest an important role of a novel group of neurons , which are neither neuropeptide Y/agouti-related peptide (NPY/AgRP) nor proopiomelanocortin (POMC) neurons in the arcuate nucleus, but are marked by the expression of Cre recombinase driven by rat insulin II promoter (Rip-Cre neurons). However, the function of Rip-Cre neurons remains unclear due to confounding effects from pancreatic islets. Moreover, the primary neurotransmitter from these neurons and its direct downstream targets are unknown. Our preliminary data show that GABA release from Rip-Cre neurons is critical for the regulation of energy expenditure and glucose homeostasis. Interestingly, Rip-Cre neurons provide intense projections to the paraventricular hypothalamus (PVH). Given the prominent role of PVH neurons in the regulation of energy balance, the GABAergic projection from Rip-Cre neurons to PVH neurons may be important in mediating the role of Rip-Cre neurons. To test the hypothesis that GABA released from Rip-Cre neurons (most of which are located in the arcuate) and its action on PVH neurons have important functions in the regulation of energy balance, the following 3 specific aims will be tested. The first specific aim is to test the hypothesis that GABA release from Rip-Cre neurons is required for the regulation of energy balance. The second specific aim is to test the hypothesis that arcuate Rip-Cre neurons send direct GABAergic projections to the PVH, and the third specific aim is to test the hypothesis that GABAergic input to PVH neurons is required for the regulation of energy balance. The proposed studies will most likely identify novel neurocircuitry that are critical for the regulation of energy expenditure and glucose homeostasis. Given the similarity in central mechanism between mice and humans, the data generated from these studies will ultimately provide part of framework for developing novel prevention and therapeutic methods for human obesity.